VMED 5172 - Receptors of Innate Immune System

Inflammation

What is a general term for the local accumulation of fluid, plasma proteins and WBCs that is initiated by physical injury, infection, or a local immune response?

Pain, redness, heat, and swelling (+loss of function)

What are the markers of inflammation in a tissue?

• To contain, destroy and remove a foreign substance or infectious agent

• To bring the tissue back to its normal state

What is the purpose of inflammation?

- Molecules conserved between many different organisms (often cell wall or DNA/RNA component)

- Integral part essential for pathogen survival

- Not found in animal tissues

- Recognized by sentinel cells

What are the major attributes of pathogen associated molecular patterns (PAMPs)?

Lipopolysaccharide/LPS/endotoxin

What is a PAMP that is a component of Gram negative bacteria cell membranes?

Peptidoglycans, lipoteichoic acids

What is a PAMP that is a component of Gram positive bacteria cell membranes?

Cell wall glycolipids, carbohydrates

What is a PAMP that is a component of acid fast bacteria cell walls?

CpG DNA (multiple C-G repeats, unmethylated)

What is a PAMP that can be targeted in the DNA of bacteria?

Cell wall carbohydrates (ex. mannose, zymosan)

What are PAMPs that can be targeted in fungi?

Viral nucleic acids (ssRNA, dsRNA, ssDNA, dsDNA)

What is a PAMP that can be targeted for viruses?

PAMPs are present on broad classes of antigens, while antigens are very specific to one type of cell/pathogen

What is the difference between a PAMP and an antigen/epitope?

Damage-associated molecular patterns (DAMPs)

What are the endogenous equivalents to PAMPs that allow for the generation of an immune response even in the absence of a microbe?

- Dying or damaged cells

- Secreted by sentinel cells

What cells exhibit DAMPs?

Recruit and activate other innate immune cells, promote tissue repair

What do DAMPs signal to happen?

- Fibrinogen, heparan sulfate

- Heat shock proteins

- Mitochondrial reactive oxygen species, Mitochondria DNA

- Defensins, Cathelicidins (antimicrobial molecules)

- Histones and DNA

What are some examples of DAMPs?

Sentinel cells

What refers to a a group of tissue-resident cells that are typically the first ones to contact invaders (macrophages, dendritic cells, mast cells)?

pattern recognition receptors (PRRs)

Sentinel cells express large numbers of ___________________ that provide the initial host response to infection or damage

Macrophages/monocytes

What are the sentinel cells that phagocytize and kill organisms, process and present antigens to T-cells, and release cytokines to recruit more cells to a site?

Dendritic cells

What are the sentinel cells that are similar to macrophages and are the most efficient antigen presenting cells (+releasing cytokines when presenting to T-cells?

Mast cells

What are the sentinel cells scattered throughout the body (under epithelial surfaces, close to blood vessels) that degranulate in response to non-specific stimuli and have a major role in mediating immunity to parasites, hypersensitivity, and antimicrobial defence?

Surface-bound IgE

Mast cells can also degranulate in an antigen-specific manner via _____________________

gene transcription

Binding of PAMPs or DAMPs to PRRs induces _______________ in sentinel cells

Initial stages of acute inflammatory response

- Cytokine release

- Chemokine release

- Release and activation of vasoactive substances

- Microbial killing

What are the results of the activated gene transcription of sentinel cells?

1) produce the initial inflammatory mediators such as cytokines and chemokines

2) stimulate material internalization to be broken down (microbial intracellular killing)

3) facilitate immune cell recruitment to site of infection (chemotaxis) and produce antimicrobial molecules (activation)

What are the different types of receptor functions for immune cells?

- Toll-like receptors (TLRs)

- NOD-like receptors

- RIG-I

- MDA-5

- AIM2

- cGAS-STING

What are some of the different types of receptors that are activated by PAMPs and DAMPs to produced the initial inflammatory mediators?

Toll-like receptors (TLRs)

What PRRs recognize extracellular ligands (microbial PAMPs)?

NON-like receptors (NLRs)

What PRRs recognize intracellular (cytosolic) ligands (microbial PAMPs and cellular DAMPs)?

RIG-I and MDA-5

What PRRs recognize cytosolic viral RNA?

AIM2 and cGAS-STING

What PRR recognizes cytosolic dsDNA?

Inflammasomes

_____________________ are multiprotein complexes that are assembled by two signals through PAMPs and DAMPs to trigger cells death and inflammation (first signal from PAMPs, second signal from DAMPs)

• External membrane (plasma membrane): Extracellular targets

• Internal membrane (endosomes): Phagocytized targets

How does the location of TLRs reflect their targets?

cell activation

TLRs are often expressed as pairs (homo- or heterodimers) and ligand binding induces ____________________

TLR2

What TLR recognizes peptidoglycan in Gram positive bacterial cell walls and release proinflammatory cytokines in response to activation (TNFa, IL-6, IL-8, IL-1B)?

TLR 4

What TLR recognizes LPS components of Gram negative bacteria and release proinflammatory cytokines in response?

TLR 5

What TLR recognizes bacterial flagellin and releases proinflammatory cytokines in response?

TLR 3, TLR 7, TLR 8

What TLRs recognize viral RNA and releases Type I interferons (IFNa and IFNB) in response?

TLR9

What TLR recognizes CpG repeats (unmethylated) in bacterial DNA and release Type 1 interferons in response?

positive, negative

TLR signaling is regulated by _______________ and ___________________ regulators

excessive

Negative regulators of TLRs (ex. IRAK-M, A20) are critical in preventing _________________ inflammation

effective

Activation of PRR is critical in determining whether or not an ___________________ response is mounted against a pathogen

• Mutations in TLR4 and TLR5 have been reported in German shepherd dogs

• Increased incidence of inflammatory bowel disease • Likely related to aberrant response to commensal gut flora

• This results in a predisposition to enteric infections, as shown by diarrhea and vomiting

What is a clinical example of the impacts of mutation of TLR genes?

- TLR7 agonist: Imiquimod (Aldara®) - Antiviral; effective for papillomaviruses, some use for certain cutaneous neoplasms

- TLR4 agonist: Monophosphoryl Lipid A - Adjuvant in hepatitis and papillomaviral vaccines

- TLR4 antagonists: in development to combat septic shock (DAMPs in blood - widespread activation)

What are some of the drugs that target TLRs for a desired effect?

- Dectin 1

- Mannose receptor (MR)

- Scavenger receptors

- Complement (CR1, CR3) and Fc (FCyR1) receptors

What are some receptors that function to stimulate material internalization to be broken down (microbial intracellular killing)?

Dectin 1

What receptor triggers internalization when it recognizes beta-1,3 glucan, a component of fungal walls?

Mannose receptor (MR)

What receptor triggers internalization when it recognizes mannosylated ligands present on fungi, viruses, and bacteria?

Scavenger receptors (Class A - collagen domain, Class B - high density lipoprotein)

What receptor triggers internalization when it recognize lipoproteins on pathogens?

G-protein coupled receptors (GPCRs)

What kinds of receptors function by facilitating immune cell recruitment to a site of infection (chemotaxis) and producing antimicrobial molecules (activation)?

Formyl peptide receptors

What GCPRs recognize fMet-Leu-Phe on DNA produced by bacteria and mitochondria?

Chemokine receptors

What GCPRs recognize CXC and CC chemokines (recruitment of more cells)?

C3a and C5a receptors

What GCPRs recognize C3a and C5a?

Cytokines

What are low molecular weight proteins that bind specific cell receptors and initiate intracellular signaling pathways and act in an autocrine/paracrine manner?

interleukins (IL-1, IL-2...)

What class are most (not all) cytokines a part of?

• Extracellular ligand (cytokine) binding portion

• Intracellular signal transduction portion (JAK-STAT pathway)

What are the two parts of most cytokine receptors?

tyrosine

Signaling pathways of cytokines often involve the phosphorylation of _______________ residues

Tyrosine kinases

What are enzymes that can phosphorylate tyrosine?

Triggering or inhibiting gene activation

What are the two possible effects of cytokine signaling on cells?

Chemokines

What are a subset of cytokines composed of very small molecules that have the major function of recruiting other cells?

False - response is initiated in an endosome

True/False: TLR 3, 7, and 8 bind viral nucleic acid and initiate the signal from the endoplasmic reticulum

False - Mitochondria is a DAMP

True/False: Mitochondrial ROS is an example of PAMP

- CXCL10 - chemokine

- fMLF - formylMet-Leu bacteria DNA

Which of the following binds to G-protein couple receptor

- LPS

- fMLF

- ssRNA

- Peptidoglycans

- IL-2

- CXCL10

- TNF-α,

- IL-1β

True

True/False: Cytosolic viral DNA is recognized by cGAS-STING, while cytosolic viral RNA is recognized by RIG-I and MDA-5

NOD1/2 - on inside, TLRs on outside of cell

Pattern recognition structures found in the cytoplasm of host cells include

- TLR-4

- Dectin-1

- NOD1/2,

- TLR-9

pathogens

PAMPs would be found on the surface of which of the following

- skin cells

- sentinel cells

- pathogens

- blood vessel wall

PPRs

(PPRs, PAMPs, DAMPS, or PMNs) on sentinel cells bind LPS, which triggers the uptake and destruction of bacteria

True - PAMPs 1st signal

True/False: The alarming inflammasome is usually activated by two signals, the first signal from PAMP and the second one from DAMP

constriction of blood vessels

Which of the following events do not occur during the initial stage of acute inflammation

- cytokine secretion

- chemokine secretion

- microbial killing

- constriction of blood vessels

TLR-9::Peptidoglycan

Which of the following is not a match of TLR to its PAMP:

- TLR-4::LPS

- TLR-5::Flagellin

- TLR-9::Peptidoglycan

- TLR-3::dsRNA